The Gunners forward has joined the Dutch giants for the entire 2015-16 campaign after finding himself behind the likes of Olivier Giroud, Danny Welbeck and Theo Walcott to lead the line at the Emirates Stadium and scored a hat-trick for Ajax in a behind-closed-doors friendly against Qatari side Umm Salal on Monday.

Despite netting a treble on his first start for his new club, the France U21 international somehow failed to convince De Boer, whose brother Frank is the manager of the senior team, that he is capable of leading Ajax to the Eredivisie title this season.

“I heard Frank say last week that this is one of the best squads with whom he has ever worked,” the former Holland international wrote in Dutch media publication Voetbal International [via Goal].

“However, when I see Sanogo, I still have my doubts. I have still found no qualities with which you can do something,” De Boer added.

Sanogo spent the second half of last season on-loan at fellow London side Crystal Palace, however, a combination of injuries and a loss of form limited him to just three starts under manager Alan Pardew and the 22-year-old is remarkably yet to score a Premier League goal for either club.